1. Field of the Invention
The present invention relates to a signal line driving device and, more specifically, to a device for driving multiple signal lines such as image signal lines for a display device.
2. Description of the Related Art
A schematic view of a known driving device for driving multiple signal lines is disclosed in Japanese Patent Application Publication No. 2006-292807 (JP-A2006-29807), for example. In JP-A 2006-29807, according to data signals to be outputted from a data latch, according to data signals to be outputted from a data latch, each of positive gradation selectors SEL1, 3, etc. selectively outputs one voltage from a set of multiple positive voltages, or each of negative gradation selectors SEL2, 4, etc. selectively outputs one voltage from a set of multiple negative voltages. The voltages are then inputted respectively into amplifiers AMP1, 3, etc. for the positive gradation and amplifiers AMP2, 4, etc. for the negative gradation. These amplifiers output gradation output signals depending on the predetermined drive capabilities of the amplifiers, and the output signals are then supplied to output terminals S1, S2, etc. through switches SW11, etc. Here, the driving device is provided with the set of the positive voltages and the set of the negative voltages so as to be applied to a display device of alternate current drive type, as typified by a display device using liquid crystal materials, for example. More specifically, the set of the positive voltages are higher than a predetermined voltage ½AVDD, while the set of the negative voltages are lower than that. The amplifiers AMP1, 3, etc. for the positive gradation are arranged in parallel to an array of the output terminals S1, S2, etc., and commonly connected to a power source wire AVDD and a ground wire AGNDP that are extending along the array of the amplifiers AMP1, 3, etc. Similarly, the amplifiers AMP2, 4, etc. for the negative gradation are arranged to be parallel to the array of the output terminals and to be adjacent to the array of the amplifiers for the positive gradation in the back and forth direction, and are also commonly connected to the power source wire AVDDN and the ground wire AGND that are extending along the amplifiers AMP2, 4, etc. According to input from the selectors, the amplifiers for the positive gradation each generate a positive output signal that is higher than a reference voltage, while the amplifiers for the negative gradation each generate a negative output signal that is lower than the reference voltage. The switches SW11, etc perform a switchover between the positive and negative output signals to alternately output these signals from output terminals adjacent to each other. Consequently, the positive and negative output signals are alternately outputted from the output terminals S1, S2, etc.
According to a review of the inventor of this application, a drive circuit of JP-A 2006-29807 mentioned above has a risk that the output signals may be made unstable due to fluctuations in source voltages caused by resistance components of a power source wire connected to the amplifier. In other words, when an amplifier AMP1 supplies an output signal of positive gradation voltage to an output terminal S1, for example, a large current has to flow from the power source wire AVDD to the output terminal S1. In contrast, no current flows from the amplifier AMP1 to a ground wire AGNDP, or some transient current or some penetration current flows, depending on performance of the amplifier. This also applies to other amplifiers AMP3, 5, etc., for the positive graduation voltages. Thus, a large current from the power source wire AVDD in concentration is supplied to the AMP1, 3, 5, etc., and thereby causes a voltage drop in the power source wire AVDD. On the other hand, when an amplifier AMP2 supplies an output signal of negative graduation voltage to an output terminal S2, for example, a large current has to flow from the output terminal S2 to the ground wire VGND, while no or slight current flows from the power source wire AVDDN to the amplifier AMP2. This also applies to other amplifiers AMP4, 6, etc. for the negative graduation voltages. Thus, the currents from the AMP2, 4, 6, etc. concentrate on the ground wire AGND, and the large current causes a voltage rise in the ground wire AGND. As such, the voltage drop in the power source wire and the voltage rise in the ground wire occur and result in noise of the power source. Consequently, the output terminals S1, etc. output the output signals having unstable potentials. In particular, a device for driving signal lines of a display device such as an LCD driver or the like tends to have a larger and larger number of output signal lines. For example, the number of output signal lines is conventionally about 240 channels, but nowadays the number has increased to a maximum of 960 channels. Thus, in a configuration and layout of a circuit having multiple output amplifiers, the effect of a voltage drop due to resistance components of the power source wire is considered to be increasingly significant as the number of outputs increases.